Marine Weather Net

Southwestern Puerto Rico out 10NM Marine Forecast


TODAY

SE
WINDS
15 - 20
KNOTS

TONIGHT

E
WINDS
15 - 20
KNOTS

SUNDAY

E
WINDS
5 - 10
KNOTS

SUNDAY NIGHT

NE
WINDS
10 - 15
KNOTS

The Marine Weather Forecast In Detail:
AMZ745 Forecast Issued: 400 AM AST Sat Jul 20 2024

SMALL CRAFT SHOULD EXERCISE CAUTION
Today...East Winds 10 To 15 Knots, Becoming Southeast 15 To 20 Knots Late This Morning And Afternoon. Seas 3 To 5 Feet, Occasionally To 6 Feet. Wave Detail: Southeast 3 Feet At 5 Seconds And East 1 Foot At 2 Seconds. Isolated Showers.
Tonight...East Winds 15 To 20 Knots, Diminishing To 10 To 15 Knots After Midnight. Seas 2 To 4 Feet, Occasionally To 5 Feet. Wave Detail: Southeast 3 Feet At 6 Seconds And Northeast 1 Foot At 2 Seconds.
Sunday...East Winds 5 To 10 Knots, Becoming Southeast In The Afternoon. Seas 2 To 3 Feet, Occasionally To 4 Feet. Wave Detail: South 2 Feet At 7 Seconds And Northeast 1 Foot At 4 Seconds.
Sunday Night...Northeast Winds 10 To 15 Knots, Diminishing To 5 To 10 Knots After Midnight. Seas 2 To 3 Feet, Occasionally To 4 Feet. Wave Detail: North 2 Feet At 4 Seconds And South 2 Feet At 6 Seconds.
Monday...East Winds Around 5 Knots, Increasing To 10 To 15 Knots With Gusts Up To 20 Knots In The Afternoon. Seas 2 To 3 Feet, Occasionally To 4 Feet. Wave Detail: South 2 Feet At 6 Seconds And North 1 Foot At 2 Seconds. Numerous Showers In The Afternoon.
Monday Night...East Winds 10 To 15 Knots, Diminishing To 5 To 10 Knots After Midnight. Seas 2 To 3 Feet, Occasionally To 4 Feet. Wave Detail: Southeast 2 Feet At 6 Seconds And North 1 Foot At 5 Seconds.
Tuesday...East Winds 10 To 15 Knots, Becoming Southeast 15 To 20 Knots In The Afternoon. Seas 2 To 3 Feet, Occasionally To 4 Feet, Building To 3 To 5 Feet, Occasionally To 6 Feet In The Afternoon. Scattered Showers In The Afternoon.
Tuesday Night...East Winds 15 To 20 Knots, Diminishing To 10 To 15 Knots After Midnight. Seas 2 To 4 Feet, Occasionally To 5 Feet.
Wednesday...East Winds 5 To 10 Knots, Increasing To 15 To 20 Knots In The Afternoon. Seas 2 To 3 Feet, Occasionally To 4 Feet, Building To 3 To 5 Feet, Occasionally To 6 Feet In The Afternoon.
Wednesday Night...East Winds 15 To 20 Knots, Diminishing To 5 To 10 Knots After Midnight. Seas 3 To 4 Feet, Occasionally To 5 Feet.
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Area Forecast Discussion
National Weather Service San Juan PR
455am AST Sat July 20 2024

Synopsis
Exiting moisture from the previous tropical wave and another big pulse of Saharan Dust Air Layer will mostly result in a warm weather pattern across the region today. Although some showers might persist during the morning hours across some coastal areas, breaking clouds are forecasted by mid-morning leading the heat indices to reach heat advisory criteria. As a result a Heat Advisory is in effect from 10am to 5pm across all the coastal areas of Puerto Rico and the U.S. Virgin Islands. Similar conditions are forecast for Sunday. Windy conditions would maintain hazardous marine conditions for today.

.SHORT TERM...Today through Monday... Quick moving showers moved across the region during the overnight hours. These showers brought moderate to locally heavy rainfall and wind gusts around 25 knots. Some lightning strikes were observed near San Juan, and over the Caribbean waters. Rainfall accumulation was light across the board.

Satellite-derived precipitable water imagery show a gradient of moisture, with a moist air mass over Puerto Rico, and a drier air one already reaching the Virgin Islands. The aerosol models show a significant Saharan Air Layer also reaching the area, so skies will be hazy. This particulate will last into tomorrow, gradually clearing out late Sunday and Monday. With less clouds and rain activity than yesterday, temperatures will soar once again, with dangerous heat indices anticipated. People are advised to stay hydrated and to take break from the sun, especially with the air quality deteriorated due to the Saharan dust.

A surface high pressure centered north of the islands will also maintain the steering flow enhanced, with winds coming out of the east southeast at 20 to 25 mph, and stronger gusts. Even with the drier air mass, some showers will move through, and some activity could develop in the afternoon. Strong heating could lead to some thunderstorms as well. Tomorrow, the ridge will be stronger, and a trade wind cap inversion is expected to develop at 800 mb. Therefore, the potential for showers will significantly decrease.

On Monday, with the Saharan dust departing, some moisture will filter in from the east. In fact, precipitable water values are expected to be above normal, so showers will increase once again. The low level winds will weaken some, but will remain from the east at around 15 knots. As it is usual with this event, the morning activity will be favored across eastern Puerto Rico and the Virgin Islands, while stronger convection should fire up in the interior and west in the afternoon hours, where the risk for urban and small stream flooding will be elevated.

Long Term
Tuesday through Saturday... A seasonal pattern will be in place for the beginning of the long term. At the surface, broad high pressure will dominate the Atlantic Basin, including the Caribbean, resulting in easterly winds across the region. Embedded in the wind flow, patches of shallow moisture, with PWAT (Precipitable Water) around 1.7 to 2 inches, will move in and out of the area from Tuesday through Wednesday. Under this pattern, the islands will primarily experience the typical weather pattern with variable mornings between warm conditions and some isolated showers, followed by afternoon convection over the western interior sections of Puerto Rico. From late Wednesday into early Thursday, a slot of drier airmass will move in but not last long, as a wind surge reaches the islands, increasing the sustained surface winds and the potential for shower development. Combining the wet pattern on Thursday, model guidance indicates some instability provided by the divergence side of an upper-level trough of an upper-low just over the western Atlantic. The outcome will be a more favorable scenario for more widespread shower activity. However, given the windy conditions, fast-moving showers might not accumulate significant rainfall in most areas.

After that wind surge, the NASA Goddard Earth Observing System Model V5 suggests another round of a Saharan Dust event. Similar to the past week's event, this will be moderate, with optical depth concentration between 0.2-0.3. This pattern will erode most available moisture, limiting the shower activity. For the same period, the dominant feature will be the surface high pressure just over the Central Atlantic, resulting in an east-southeasterly wind flow. As usual during the summer days in Puerto Rico and the U.S. Virgin Islands, warmer conditions with Saharan Dust particles will increase heat index values across the region. Excessive heat products are forecasted for those days.

Marine
A broad surface high pressure over the Central Atlantic will continue to promote moderate to locally fresh easterly winds across the local waters, resulting in choppy seas. As a result, several small craft advisories will remain in effect until 6pm today. For tonight, winds will diminish to 10-15 knots for the rest of the period. Afternoon convection over the Mona Channel might result in localized hazardous marine conditions each day.

Beach Forecast
Windy conditions provided by surface high pressure over the Central Atlantic will promote breezy conditions across the coastal areas of the islands. These conditions might turn choppy at the beach, occasionally resulting in slightly higher seas. There is a high risk of rip currents for St. Croix beaches, but a moderate risk of rip currents will be present for other areas.

.SJU WATCHES/WARNINGS/ADVISORIES... PR...
Heat Advisory from 10am this morning to 5pm AST this afternoon for PRZ001>003-005-007-008-010>013.

VI...
Heat Advisory from 10am this morning to 5pm AST this afternoon for VIZ001-002.

High Rip Current Risk through this afternoon for VIZ002.

AM...Small Craft Advisory until 6pm AST this evening for AMZ711-712- 723-733-741.

Small Craft Advisory until 6pm AST this evening for AMZ716.